1. Field of the Invention
The present invention relates to a multi-phase (referred to as a xe2x80x9cP-phasexe2x80x9d in this specification) electric rotating machine having toroidal coils such as a P-phase stepping motor having toroidal coils that is adequate for a driving motor of an ink-jet printer, a copier or the like.
2. Description of Prior Arts
Several types of stepping motors are known as prior arts in this kind of use. FIG. 13 is perspective view showing a claw pole permanent magnet type (referred to as a xe2x80x9cPM-typexe2x80x9d in the following description) stepping motor as a first prior art.
In FIG. 13, a stator S consists of a first stator unit 101 and a second stator unit 102 that make up a two-phase construction. The first stator unit 101 consists of comb-shaped shaped stator teeth 101a, 101b that arranged by turns along the inner circumference thereof, and a toroidal coil 101c that is housed in these stator teeth 101a, 101b. In the same manner, the second stator unit 102 consists of comb-shaped stator teeth 102a, 102b and a toroidal coil 102c that is housed in these stator teeth 102a, 102b. 
Here, the stator teeth 101a and 102a are arranged with difference of 90 degrees in electric angle, for example.
The reference symbol R represents a rotor, which consists of a permanent magnet 103 whose outer circumference is magnetized such that N and S poles are alternatively arranged in the circumferential direction, a yoke 104 and a rotating shaft 105. The rotating shaft 105 is supported by the stator S through a bearing.
In this case, the angular pitch of the stator teeth in each stator unit of the stator S and the angular pitch of the N and S poles of the rotor R are determined to be coincident with each other.
Since the coils of the claw pole PM type stepping motor are formed by winding wires on bobbins, a time needed for winding wire is relatively short and connection wires can be easily attached, which can reduce the manufacturing cost. Therefore, this type of stepping motor is widely used in office automation equipment or the like.
FIG. 14 is a partially sectional perspective view showing a principal portion of a hybrid type (referred to as a xe2x80x9cHB-type xe2x80x9d in the following description) stepping motor as a second prior art.
In FIG. 14, the reference numeral 15 represents a rotating shaft, 17 represents a stator pole, 18 and 19 represent rotor teeth of a pair of rotor units.
Since the HB-type stepping motor allows the stator and the rotor to have a large number of pole teeth, step angle can be kept small, which gives advantages in positioning accuracy and in low-speed stability. Therefore, this type of stepping motor is also widely used in office automation equipment such as a printer or a copier.
In this construction, the coils of the stator are wound on the stator poles through slots formed at the inside portion of the stator, and therefore a two phase motor requires eight coils because the two-phase motor is provided with eight stator poles in general, as shown in FIG. 14.
The above described conventional constructions have problems as follows.
The PM-type stepping motor, which is the first prior art shown in FIG. 13, is produced at low !price because of the bobbin winding construction, while it is difficult to increase a number of magnetic poles because the stator teeth of the stator are formed as the claw poles (i.e., the comb teeth) that are meshed by turns and the rotor is magnetized. In general, the PM-type stepping motor whose motor diameter is about 40 mm has twenty-four magnetic poles, and resolution (i.e., step angle) of the two-phase motor is about 7.5 degrees.
Further, in the claw pole stator, since a magnetic flux is concentrated at the root of the claw pole, a magnetic flux density becomes saturated at the root of the claw pole, which produces a reduction of torque.
Still further, when the claw pole stator is adapted, since the stator teeth are meshed by turns, a leakage flux between the claw poles becomes larger.
On the other hand, the HB-type stepping motor, which is the second prior art shown in FIG. 14, has high resolution, while it has disadvantages that a time needed for winding wire is relatively long and a setting of connection wires is complex and expensive, because it is difficult to wind the stator coil wire through the narrow slot formed at the inside portion of the stator.
Further, though a magnetic flux generated from a permanent magnet of the rotor flows to the stator tooth faced thereto, the ratio of effective magnetic flux interlinkage with the coil is about 50%, which requires an expensive permanent magnet having a strong magnetic flux in order to keep adequate torque. This phenomenon will be described with reference to FIG. 15.
FIG. 15 is an enlarged view of the stator pole 17, the rotor tooth 18 that is S pole and the rotor tooth 19 that is N pole, which are shown in FIG. 14.
The rotor teeth 18 and 19 are arranged with difference of half-pitch.
A magnetic flux xcfx861 exited from the rotor tooth 18 is divided into a magnetic flux xcfx862 that returns to the adjacent rotor tooth 19 and a magnetic flux xcfx863 interlinkage with the coil. Since the returning magnetic flux xcfx862 is a half of the magnetic flux xcfx861, the effective magnetic flux xcfx863, which produces torque, becomes the remaining half of xcfx861.
It is therefore an object of the present invention to provide a P-phase electric rotating machine having toroidal coils that solves the foregoing problems and using method thereof.
In order to achieve the above object, a P-phase electric rotating machine having toroidal coils of the present invention is constructed as follows.
According to a first aspect of the present invention, provided is a P-phase electric rotating machine comprising: a stator including the number P of stator units (P is integer satisfying Pxe2x89xa72) each of which is formed of a pair of stator iron cores made from magnetic material and a toroidal coil that concentrically gets caught between the pair of stator iron cores, each of the stator iron cores being provided with the number Ns of stator teeth formed around an inner circumference at equal pitch Ps, the pair of stator iron cores of the each stator unit being arranged such that the stat br teeth are shifted to each other by xc2xd of the pitch Ps, and the number P of stator units being concentrically connected to be arranged in a direction of a rotating shaft such that the stator teeth of the stator units are shifted to one another by xc2xd P of the pitch Ps; and a rotor that faces the stator with a predetermined air gap and is rotatable, the rotor consisting of at least one rotor unit that has a permanent magnet and rotor teeth of Nr in the total number made from magnetic material arranged around the permanent magnet in the rotating direction of the rotor, the rotor teeth consisting of k pair of N (north) and S (south) polar rotor teeth groups (k is integer satisfying kxe2x89xa71) arranged in the rotating direction, the each N polar rotor teeth group consisting of the number (Nr/2k) if rotor teeth that are continuously arranged in the rotating direction, and the each S polar rotor teeth group consisting of the number (Nr/2k) of rotor teeth that are continuously arranged in the rotating direction.
According to a second aspect of the present invention, in the P-phase electric rotating machine according to the first aspect of the present invention, the rotor comprises the number P of independent rotor units that correspond to and face the stator units, respectively.
According to a third aspect of the present invention, in the P-phase electric rotating machine according to the second aspect of the present invention, the number P of stator units are arranged such that the stator teeth of the stator units are coincident with one another instead of shifting, and the number P of rotor units are arranged such that the rotor teeth of the rotor units are shifted to one another by xc2xd P of the pitch Ps.
According to a fourth aspect of the present invention, provided is a P-phase electric rotating machine comprising: the number P of independent stator units (P is integer satisfying Pxe2x89xa72) each of which is formed of a pair of stator iron cores made from magnetic material and a toroidal coil that concentrically gets caught between the pair of stator iron cores, each of the stator iron cores being provided with the number Ns of stator teeth formed around an inner circumference at equal pitch Ps, the pair of stator iron cores of the each stator unit being arranged such that the stator teeth are shifted to each other by xc2xd of the pitch Ps, and the stator units being arranged in a direction of a rotating shaft; and the number P of independent rotor units that face the stator units with a predetermined air gap, respectively, and are rotatable, the rotor unit having a permanent magnet and rotor teeth of Nr in the total number made from magnetic material arranged around the permanent magnet in the rotating direction of the rotor, the rotor teeth consisting of k pair of N (north) and S (south) polar rotor teeth groups (k is integer satisfying kxe2x89xa71) arranged in the rotating direction, the each N polar rotor teeth group consisting of the number (Nr/2k) of rotor teeth that are continuously arranged in the rotating direction, and the each S polar rotor teeth group consisting of the number (Nr/2k) of rotor teeth that are continuously arranged in the rotating direction, wherein when one phase of the toroidal coils of the stator units is excited and the corresponding rotor unit is attracted and aligned, the stator,teeth of the stator unit of the next phase is shifted from the rotor teeth of the corresponding rotor by xc2xd P of the pitch Ps.
According to a fifth aspect of the present invention, in the P-phase electric rotating machine according to one of the first through fourth aspects of the present invention, the stator teeth of the stator units overhang the inner circumference of the toroidal coils.
According to a sixth aspect of the present invention, in the P-phase electric rotating machine according to one of the first through fourth aspects of the present invention, the average center line of the N polar rotor teeth group forms (360(nxc2x1xc2xd)/Ns) degrees (n is integer satisfying nxe2x89xa71) with respect to the average center line of the S polar rotor teeth group.
According to a seventh aspect of the present invention, in the P-phase electric rotating machine according to one of the first through fourth aspects of the present invention, Nr is smaller than Ns.
According to a eighth aspect of the present invention, in the P-phase electric rotating machine according to one of the first through fourth aspects of the present invention, P, k and Ns satisfy the conditions P=2, k=2 and Ns=4nxc2x12.
According to a ninth aspect of the present invention, in the P-phase electric rotating machine according to one of the first through fourth aspects of the present invention, rotor magnetic bodies of the different polar rotor teeth groups are alternatively arranged around the rotor, and the boundaries among the different polar rotor teeth groups are connected to form a one-piece body at least when it is laminated.
It should be noted that a iron core of the rotor is referred to as the rotor magnetic body in this specification in order to distinguish the rotor elements from the stator elements.
According to a tenth aspect of the present invention, in the P-phase electric rotating machine according to one of the first through fourth aspects of the present invention, the stator unit is provided with a bobbin on which the toroidal coil is wound, and the bobbin gets caught between the pair of stator iron cores.
According to a eleventh aspect of the present invention, in the P-phase electric rotating machine according to one of the first through fourth aspects of the present invention, the stator teeth or the rotor teeth are formed as claw poles by die-cutting a magnetic steel plate.
According to a twelfth aspect of the present invention, in the P-phase electric rotating machine according to the eleventh aspect of the present invention, a yoke portion made from magnetic material is further provided, the yoke portion is closely connected with the outer circumference of the claw poles of the stator or the inner circumference of the claw poles of the rotor, and the yoke portion is independent from or integral with the stator or rotor.
According to a thirteenth aspect of the present invention, in the P-phase electric rotating machine according to one of the first through fourth aspects of the present invention, the rotor is arranged to surround the stator as an outer rotor construction, the stator teeth are formed around outer circumference instead of the inner circumference, and the rotor teeth are formed around inner circumference of the permanent magnet instead of the outer circumference.
According to a fourteenth aspect of the present invention, in the P-phase electric rotating machine according to one of the first through fourth aspects of the present invention, the motor is applied to an actuator to carry a printing head or to feed sheet in a printer.